Bicycle Mechanics - Cassettes - Which material wears faster?

titanium, steel, or others?

The answer to this is directly related to the specific hardness of each material.

Aluminium is the softest material that I am aware of in use as cogs.

Ti is the hardest, and steel sits nicely (and inexpensively) in the middle.

The answer to this is directly related to the specific hardness of each material.

Aluminium is the softest material that I am aware of in use as cogs.

Ti is the hardest, and steel sits nicely (and inexpensively) in the middle.
Steel can be hardened much more than titanium. I'd say steel is the best material.

I've used the DuraAce ti cassette. It wore out pretty quickly. I went back to the all-steel Ultegra for increased durability. Aluminum cassettes are special for racing only. They wear super quick.

Chain rings seem to be made of aluminium fairly often.

You want a cassette that wears out fast? Most of the non-steel cassettes will fall into that category. If you absolutely need to shave a few tens of grams you can buy an aluminum cassette that will be good for about 1000 miles; titanium versions are not that much better for longevity.

It also depends on the size of the cog. On Dura-Ace cassettes, only the largest few cogs are ti, because larger cogs wear more slowly than small ones (all other things being equal). A titanium 11-tooth cog wouldn't last very long at all.

That's why you can make chainrings out of aluminum without any trouble. They're just much bigger. Steel and titanium chainrings only make sense when it comes to granny gears on mountain bikes.

Campy used to make an all aluminum freewheel. It was light, but it barely held up long enough to ride out of the bike shop parking lot.

I think the manufacturers are not trying all that hard to be honest. Stuff that is light, wears out fast and costs alot makes these companies lots of money. There are Ti and aluminum alloys that are harder than the steel they are making cogs out of now. Maybe the cost is prohibitive, but it could be done. There are some car engine blocks made of aluminum alloy that last as long as cast iron blocks, for example. Such material may be too brittle for cogs, but there literally hundreds of alloys available to manufacturers.

Ally blocks usually have steel liners, or even ceramic ones.

I think the manufacturers are not trying all that hard to be honest. Stuff that is light, wears out fast and costs alot makes these companies lots of money. There are Ti and aluminum alloys that are harder than the steel they are making cogs out of now. Maybe the cost is prohibitive, but it could be done. There are some car engine blocks made of aluminum alloy that last as long as cast iron blocks, for example. Such material may be too brittle for cogs, but there literally hundreds of alloys available to manufacturers.

As a machinist I have machined many different alloys of aluminum and steel and have yet to see an aluminum alloy that is harder then any of the steels I have cut. All of the titanium I have worked with is harder to machine then soft steel but it is actually softer (will dent easier).

Does anyone know if the steel cogs are heat treated?

Ally blocks usually have steel liners, or even ceramic ones.D'oh?

D'oh?

???

As a machinist I have machined many different alloys of aluminum and steel and have yet to see an aluminum alloy that is harder then any of the steels I have cut. All of the titanium I have worked with is harder to machine then soft steel but it is actually softer (will dent easier).

Does anyone know if the steel cogs are heat treated?
Pretty much all steel is heat treated. If you're talking about how hard it is, I'm no expert, but I would venture to say that the cogs are on the upper end of the hardness spectrum. They don't have to be especially tough, so there's no reason not to harden them...

Pretty much all steel is heat treated. ..Not really.

............. but I would venture to say that the cogs are on the upper end of the hardness spectrum. They don't have to be especially tough, so there's no reason not to harden them...What???

Ally blocks usually have steel liners, or even ceramic ones.

True, but some don't. I believe some manufacturers use an alloy with alot of silica in it.

Does anyone know if the steel cogs are heat treated?


I would think they would be, but I have no idea. It would be really simple and cheap to case harden them by quenching in oil or water, so I would expect that they are. Anyone have access to a brinnel hardness tester? I'd be currious to know how hard steel cogs are.

I would think they would be, but I have no idea. It would be really simple and cheap to case harden them by quenching in oil or water, so I would expect that they are. Nope. AFWIW, case hardening isn't a simple oil or water quench.

If you want something that wears fast, go buy a dura ace cassette.

I am not a materials expert, but my basic understanding is: titanium alloy is stronger than steel; pure titanium probably is not as strong as steel; titanium alloy is a lot harder to machine because it is so tough (and that is why it is more expensive); pure titanium is a lot easier to work with but is not used very much; and, you probably do not have to worry about excessive wear of titanium cogs unless you start to see sparks flying from your freewheel. :)

I have some materials background. Shimano will not give out any information but is is fairly easy to deduce. Titanium. I have noticed that on a few dura-ace cassettes, there is rust on them. Since the cassettes are made in Japan, looking at viable titanium suppliers, they are using Russian titanium. The Russians do not have the technology (triple-vacuum melting) that we do - therefore the "purity" of their Ti cannot match that of US and therefore, that is one explanation for the rusting (impurities in the titanium). Next, looking at machinability, and cost... looking at both of these factors, one can deduce that Shimano is using CP2 (Commercially Pure grade 2 titanium) which is non-hardenable. Shimano claims Nickel-plating on their Dura-Ace steel cogs. Without actually Rockwell testing for hardness I would deduce they are using a mild inexpensive steel/non heat treated and using the nickel plating (because it is less expensive than using and heat treating a higher quality steel - knife makers do this as well). The nickel plating increases wear resistance and insulates the steel from the elements, preventing rusting. That is my 2 cents :-)

titanium is not stronger than steel. period. its strength to weight ratio is better, but htat's irrelevant in cogs (same size). Titanium is hard to machine becuase of its properties (bad cconductance etc) not because it is tougher or harder..

Nope. AFWIW, case hardening isn't a simple oil or water quench.

Why not? It can indeed be that simple.

CP titanium has only 35,000 pounds or so tensile strength. Also, by being soft, it is "gummy" and tends to gum-up the cutters on milling machines. Titanium alloys approach the strenghts of some of the better stainless steels. We have heat treated Beta-C titanium to RC50 - which is approaching 260,000 pounds tensile strength. I believe the highest strength metal is Nitinol 60 (a Nickel/Ti alloy). We have heat treated to RC70 ! And it was not brittle. I think I have the only remaining supply :-)

Why not? It can indeed be that simple.Depending on the steel being hi or low carbon.

Right you are sydney

I would assume that the higher cost of titanium is simply supply vs. demand. Titanium is in constant demand by the aircraft industry due to its light weight and heat resistance. Iron and carbon used to make steel are in vast supply. There are so many different grades of steel it seems ludicrous to try to make generalized comparisons of "steel" to other alloys.
I recently found that a 16t steel cog that I had mixed in with other steel and titanium cogs on a custom cassette had worn out after relatively few miles, maybe 2000 mi. The older Ultegra cogs and Dura-Ace cogs on the same cassette showed hardly any wear. The steel in the 16 just wasn't as good as the other cogs. The 16 was a no-name Shimano type cog.
My wife and I have put many thousands of miles on Ultegra and Dura-Ace cogs. I don't know which are the more wear resistant. Between the two I would make a choice based on how much hill climbing I plan to do, or simply how much money I want to spend. I know that 105 cogs are good too.

Al

As a machinist I have machined many different alloys of aluminum and steel and have yet to see an aluminum alloy that is harder then any of the steels I have cut. All of the titanium I have worked with is harder to machine then soft steel but it is actually softer (will dent easier).

Does anyone know if the steel cogs are heat treated?

It depends on what group you buy, some are also plated. They are not all the same. You get what you pay for in most cases.

Things can change from year to year. However the 2003 trade support manual gives a vague explanation. It was on an older web site. It calls out the Ti cogs on Dura Ace. It says the bottom two or three sprockets depending on size, are Ti and the rest are nickel plated chrome-molly.
The Dura Ace chain rings are nickel plated aluminum.

Chrome plated cogs on Ultegra. (all steel) but no mention of chrome molly from Ultegra on down, must be a less expensive alloy.. Pearl bright finish on 105, whatever that is, it does look different. And Nickel plated on Tiagra and Sora for example. I thought I read something about heat treating, but I can' t find it right now. There's no mention of plating of Ultegra on down for the chain rings. I have to assume they are not. They don't look it.

I would hope the cogs are least case hardened? If I find it I'll post it.

Depending on the steel being hi or low carbon.

Of course, but even mild steels can be surface hardened by quenching. That would be a big improvement in this application.

Of course, but even mild steels can be surface hardened by quenching. That would be a big improvement in this application.

To case harden low carbon steel carbon needs to be added during the heat treat process. High carbon tool steels can be hardened by quenching in water, oil, or even air cooled depending on the steel type.


Pretty much all steel is heat treated. If you're talking about how hard it is, I'm no expert, but I would venture to say that the cogs are on the upper end of the hardness spectrum. They don't have to be especially tough, so there's no reason not to harden them...

Heat treating will make them more brittle. I think if they were at the upper end of the hardness spectrum there would be trouble with teeth snapping off.